1. Field of the Invention
The present invention pertains to a vibration damping device adapted for example for use in an automotive engine mount and relates in particular to a fluid-filled vibration damping device adapted to utilize vibration damping effect on the basis of flow action of a non-compressible fluid which has been sealed inside.
2. Description of the Related Art
Fluid-filled vibration damping devices designed for example for application in automotive engine mounts represent one type of vibration damping device known in the past. Such fluid-filled vibration damping devices are typically constructed by elastically linking through a main rubber elastic body a first mounting member that has been mounted onto a first component (a power unit etc.) making up a vibrating system and a second mounting member that has been mounted onto another component (a vehicle body etc.) making up the vibrating system. Additionally, in the interior of the fluid-filled vibration damping device, there is formed a pressure-receiving chamber whose wall is partially defined by the main rubber elastic body and an equilibrium chamber whose wall is partially defined by a flexible film, the pressure-receiving chamber and the equilibrium chamber being filled with a non-compressible fluid, and the pressure-receiving chamber and the equilibrium chamber communicating with one another through an orifice passage. At times of vibration input, relative pressure fluctuations of the pressure-receiving chamber and the equilibrium chamber will give rise to fluid flow through the orifice passage, producing vibration damping effect on the basis of flow action of the fluid.
In such fluid-filled vibration damping devices, the orifice passage is pre-tuned to the frequency of the particular type of vibration targeted for damping, and produces excellent vibration damping effect against vibration having this tuning frequency. On the other hand, it has proven difficult to produce effective vibration damping effect against vibration of frequencies different from the tuning frequency of the orifice passage.
There has accordingly been proposed inter alia in US-A-2007-0013115 a structure in which a first orifice passage is formed connecting the pressure-receiving chamber and the equilibrium chamber, an intermediate chamber is formed in the interior of a partition member that separates the pressure-receiving chamber and the equilibrium chamber, and a second orifice passage is formed connecting the pressure-receiving chamber with the intermediate chamber. With such a structure, by tuning the second orifice passage to a higher frequency than the first orifice passage for example, it is possible to obtain vibration damping effect against vibration of multiple different frequencies.
In the construction disclosed in US-A-2007-0013115, a moveable rubber film is arranged in the dividing wall section between the pressure-receiving chamber and the intermediate chamber which lie on the flow path of the second orifice passage, and at times of input of low-frequency, large-amplitude vibration, fluid flow through the second orifice passage, which has been tuned to high frequency, will be limited by the elasticity of this moveable rubber film. As a result, fluid flow will be effectively produced through the first orifice passage, which has greater flow friction than the second orifice passage. At times of input of high-frequency, small-amplitude vibration, liquid pressure of the pressure-receiving chamber will be transmitted to the intermediate chamber through minute deformation of the moveable rubber film so as to give rise to fluid flow through the second orifice passage between the pressure-receiving chamber and the intermediate chamber.
However, with the fluid-filled vibration damping device disclosed in US-A-2007-0013115, because the moveable rubber film is arranged on the flow path of the second orifice passage, there is a risk that fluid flow through the second orifice passage will be limited by the elasticity of the moveable rubber film even at times of input of vibration in the frequency range to which the second orifice passage has been tuned, thus preventing fluid flow through the second orifice passage from giving rise to sufficient vibration damping effect.
Moreover, recent more compact vehicle sizes impose severe limitations on installation space for fluid-filled vibration damping devices, and in association there has arisen stronger demand for more compact fluid-filled vibration damping devices. However, it has been shown that as fluid-filled vibration damping devices are made more compact in size, the vibration damping effect afforded by the second orifice passage may be diminished further, and may prove insufficient in some instances.